/**
 * MIT License
 *
 * Copyright (c) 2017 Thibaut Goetghebuer-Planchon <tessil@gmx.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
#ifndef TSL_HOPSCOTCH_HASH_H
#define TSL_HOPSCOTCH_HASH_H

#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstddef>
#include <cstdint>
#include <functional>
#include <initializer_list>
#include <iterator>
#include <limits>
#include <memory>
#include <new>
#include <stdexcept>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>

#include "hopscotch_growth_policy.h"

namespace collie {
namespace detail_hopscotch_hash {

template <typename T>
struct make_void {
  using type = void;
};

template <typename T, typename = void>
struct has_is_transparent : std::false_type {};

template <typename T>
struct has_is_transparent<T,
                          typename make_void<typename T::is_transparent>::type>
    : std::true_type {};

template <typename T, typename = void>
struct has_key_compare : std::false_type {};

template <typename T>
struct has_key_compare<T, typename make_void<typename T::key_compare>::type>
    : std::true_type {};

template <typename U>
struct is_power_of_two_policy : std::false_type {};

template <std::size_t GrowthFactor>
struct is_power_of_two_policy<collie::hh::power_of_two_growth_policy<GrowthFactor>>
    : std::true_type {};

template <typename T, typename U>
static T numeric_cast(U value,
                      const char* error_message = "numeric_cast() failed.") {
  T ret = static_cast<T>(value);
  if (static_cast<U>(ret) != value) {
    TSL_HH_THROW_OR_TERMINATE(std::runtime_error, error_message);
  }

  const bool is_same_signedness =
      (std::is_unsigned<T>::value && std::is_unsigned<U>::value) ||
      (std::is_signed<T>::value && std::is_signed<U>::value);
  if (!is_same_signedness && (ret < T{}) != (value < U{})) {
    TSL_HH_THROW_OR_TERMINATE(std::runtime_error, error_message);
  }

  return ret;
}

/*
 * smallest_type_for_min_bits::type returns the smallest type that can fit
 * MinBits.
 */
static const std::size_t SMALLEST_TYPE_MAX_BITS_SUPPORTED = 64;
template <unsigned int MinBits, typename Enable = void>
class smallest_type_for_min_bits {};

template <unsigned int MinBits>
class smallest_type_for_min_bits<
    MinBits, typename std::enable_if<(MinBits > 0) && (MinBits <= 8)>::type> {
 public:
  using type = std::uint_least8_t;
};

template <unsigned int MinBits>
class smallest_type_for_min_bits<
    MinBits, typename std::enable_if<(MinBits > 8) && (MinBits <= 16)>::type> {
 public:
  using type = std::uint_least16_t;
};

template <unsigned int MinBits>
class smallest_type_for_min_bits<
    MinBits, typename std::enable_if<(MinBits > 16) && (MinBits <= 32)>::type> {
 public:
  using type = std::uint_least32_t;
};

template <unsigned int MinBits>
class smallest_type_for_min_bits<
    MinBits, typename std::enable_if<(MinBits > 32) && (MinBits <= 64)>::type> {
 public:
  using type = std::uint_least64_t;
};

/*
 * Each bucket may store up to three elements:
 * - An aligned storage to store a value_type object with placement-new.
 * - An (optional) hash of the value in the bucket.
 * - An unsigned integer of type neighborhood_bitmap used to tell us which
 * buckets in the neighborhood of the current bucket contain a value with a hash
 * belonging to the current bucket.
 *
 * For a bucket 'bct', a bit 'i' (counting from 0 and from the least significant
 * bit to the most significant) set to 1 means that the bucket 'bct + i'
 * contains a value with a hash belonging to bucket 'bct'. The bits used for
 * that, start from the third least significant bit. The two least significant
 * bits are reserved:
 * - The least significant bit is set to 1 if there is a value in the bucket
 * storage.
 * - The second least significant bit is set to 1 if there is an overflow. More
 * than NeighborhoodSize values give the same hash, all overflow values are
 * stored in the m_overflow_elements list of the map.
 *
 * Details regarding hopscotch hashing an its implementation can be found here:
 *  https://tessil.github.io/2016/08/29/hopscotch-hashing.html
 */
static const std::size_t NB_RESERVED_BITS_IN_NEIGHBORHOOD = 2;

using truncated_hash_type = std::uint_least32_t;

/**
 * Helper class that stores a truncated hash if StoreHash is true and nothing
 * otherwise.
 */
template <bool StoreHash>
class hopscotch_bucket_hash {
 public:
  bool bucket_hash_equal(std::size_t /*hash*/) const noexcept { return true; }

  truncated_hash_type truncated_bucket_hash() const noexcept { return 0; }

 protected:
  void copy_hash(const hopscotch_bucket_hash&) noexcept {}

  void set_hash(truncated_hash_type /*hash*/) noexcept {}
};

template <>
class hopscotch_bucket_hash<true> {
 public:
  bool bucket_hash_equal(std::size_t hash) const noexcept {
    return m_hash == truncated_hash_type(hash);
  }

  truncated_hash_type truncated_bucket_hash() const noexcept { return m_hash; }

 protected:
  void copy_hash(const hopscotch_bucket_hash& bucket) noexcept {
    m_hash = bucket.m_hash;
  }

  void set_hash(truncated_hash_type hash) noexcept { m_hash = hash; }

 private:
  truncated_hash_type m_hash;
};

template <typename ValueType, unsigned int NeighborhoodSize, bool StoreHash>
class hopscotch_bucket : public hopscotch_bucket_hash<StoreHash> {
 private:
  static const std::size_t MIN_NEIGHBORHOOD_SIZE = 4;
  static const std::size_t MAX_NEIGHBORHOOD_SIZE =
      SMALLEST_TYPE_MAX_BITS_SUPPORTED - NB_RESERVED_BITS_IN_NEIGHBORHOOD;

  static_assert(NeighborhoodSize >= 4, "NeighborhoodSize should be >= 4.");
  // We can't put a variable in the message, ensure coherence
  static_assert(MIN_NEIGHBORHOOD_SIZE == 4, "");

  static_assert(NeighborhoodSize <= 62, "NeighborhoodSize should be <= 62.");
  // We can't put a variable in the message, ensure coherence
  static_assert(MAX_NEIGHBORHOOD_SIZE == 62, "");

  static_assert(!StoreHash || NeighborhoodSize <= 30,
                "NeighborhoodSize should be <= 30 if StoreHash is true.");
  // We can't put a variable in the message, ensure coherence
  static_assert(MAX_NEIGHBORHOOD_SIZE - 32 == 30, "");

  using bucket_hash = hopscotch_bucket_hash<StoreHash>;

 public:
  using value_type = ValueType;
  using neighborhood_bitmap = typename smallest_type_for_min_bits<
      NeighborhoodSize + NB_RESERVED_BITS_IN_NEIGHBORHOOD>::type;

  hopscotch_bucket() noexcept : bucket_hash(), m_neighborhood_infos(0) {
    tsl_hh_assert(empty());
  }

  hopscotch_bucket(const hopscotch_bucket& bucket) noexcept(
      std::is_nothrow_copy_constructible<value_type>::value)
      : bucket_hash(bucket), m_neighborhood_infos(0) {
    if (!bucket.empty()) {
      ::new (static_cast<void*>(std::addressof(m_value)))
          value_type(bucket.value());
    }

    m_neighborhood_infos = bucket.m_neighborhood_infos;
  }

  hopscotch_bucket(hopscotch_bucket&& bucket) noexcept(
      std::is_nothrow_move_constructible<value_type>::value)
      : bucket_hash(std::move(bucket)), m_neighborhood_infos(0) {
    if (!bucket.empty()) {
      ::new (static_cast<void*>(std::addressof(m_value)))
          value_type(std::move(bucket.value()));
    }

    m_neighborhood_infos = bucket.m_neighborhood_infos;
  }

  hopscotch_bucket& operator=(const hopscotch_bucket& bucket) noexcept(
      std::is_nothrow_copy_constructible<value_type>::value) {
    if (this != &bucket) {
      remove_value();

      bucket_hash::operator=(bucket);
      if (!bucket.empty()) {
        ::new (static_cast<void*>(std::addressof(m_value)))
            value_type(bucket.value());
      }

      m_neighborhood_infos = bucket.m_neighborhood_infos;
    }

    return *this;
  }

  hopscotch_bucket& operator=(hopscotch_bucket&&) = delete;

  ~hopscotch_bucket() noexcept {
    if (!empty()) {
      destroy_value();
    }
  }

  neighborhood_bitmap neighborhood_infos() const noexcept {
    return neighborhood_bitmap(m_neighborhood_infos >>
                               NB_RESERVED_BITS_IN_NEIGHBORHOOD);
  }

  void set_overflow(bool has_overflow) noexcept {
    if (has_overflow) {
      m_neighborhood_infos = neighborhood_bitmap(m_neighborhood_infos | 2);
    } else {
      m_neighborhood_infos = neighborhood_bitmap(m_neighborhood_infos & ~2);
    }
  }

  bool has_overflow() const noexcept { return (m_neighborhood_infos & 2) != 0; }

  bool empty() const noexcept { return (m_neighborhood_infos & 1) == 0; }

  void toggle_neighbor_presence(std::size_t ineighbor) noexcept {
    tsl_hh_assert(ineighbor <= NeighborhoodSize);
    m_neighborhood_infos = neighborhood_bitmap(
        m_neighborhood_infos ^
        (1ull << (ineighbor + NB_RESERVED_BITS_IN_NEIGHBORHOOD)));
  }

  bool check_neighbor_presence(std::size_t ineighbor) const noexcept {
    tsl_hh_assert(ineighbor <= NeighborhoodSize);
    if (((m_neighborhood_infos >>
          (ineighbor + NB_RESERVED_BITS_IN_NEIGHBORHOOD)) &
         1) == 1) {
      return true;
    }

    return false;
  }

  value_type& value() noexcept {
    tsl_hh_assert(!empty());
    return *std::launder(
        reinterpret_cast<value_type*>(std::addressof(m_value)));
  }

  const value_type& value() const noexcept {
    tsl_hh_assert(!empty());
    return *std::launder(
        reinterpret_cast<const value_type*>(std::addressof(m_value)));
  }

  template <typename... Args>
  void set_value_of_empty_bucket(truncated_hash_type hash,
                                 Args&&... value_type_args) {
    tsl_hh_assert(empty());

    ::new (static_cast<void*>(std::addressof(m_value)))
        value_type(std::forward<Args>(value_type_args)...);
    set_empty(false);
    this->set_hash(hash);
  }

  void swap_value_into_empty_bucket(hopscotch_bucket& empty_bucket) {
    tsl_hh_assert(empty_bucket.empty());
    if (!empty()) {
      ::new (static_cast<void*>(std::addressof(empty_bucket.m_value)))
          value_type(std::move(value()));
      empty_bucket.copy_hash(*this);
      empty_bucket.set_empty(false);

      destroy_value();
      set_empty(true);
    }
  }

  void remove_value() noexcept {
    if (!empty()) {
      destroy_value();
      set_empty(true);
    }
  }

  void clear() noexcept {
    if (!empty()) {
      destroy_value();
    }

    m_neighborhood_infos = 0;
    tsl_hh_assert(empty());
  }

  static truncated_hash_type truncate_hash(std::size_t hash) noexcept {
    return truncated_hash_type(hash);
  }

 private:
  void set_empty(bool is_empty) noexcept {
    if (is_empty) {
      m_neighborhood_infos = neighborhood_bitmap(m_neighborhood_infos & ~1);
    } else {
      m_neighborhood_infos = neighborhood_bitmap(m_neighborhood_infos | 1);
    }
  }

  void destroy_value() noexcept {
    tsl_hh_assert(!empty());
    value().~value_type();
  }

 private:
  neighborhood_bitmap m_neighborhood_infos;
  alignas(value_type) unsigned char m_value[sizeof(value_type)];
};

/**
 * Internal common class used by (b)hopscotch_map and (b)hopscotch_set.
 *
 * ValueType is what will be stored by hopscotch_hash (usually std::pair<Key, T>
 * for a map and Key for a set).
 *
 * KeySelect should be a FunctionObject which takes a ValueType in parameter and
 * returns a reference to the key.
 *
 * ValueSelect should be a FunctionObject which takes a ValueType in parameter
 * and returns a reference to the value. ValueSelect should be void if there is
 * no value (in a set for example).
 *
 * OverflowContainer will be used as containers for overflown elements. Usually
 * it should be a list<ValueType> or a set<Key>/map<Key, T>.
 */
template <class ValueType, class KeySelect, class ValueSelect, class Hash,
          class KeyEqual, class Allocator, unsigned int NeighborhoodSize,
          bool StoreHash, class GrowthPolicy, class OverflowContainer>
class hopscotch_hash : private Hash, private KeyEqual, private GrowthPolicy {
 private:
  template <typename U>
  using has_mapped_type =
      typename std::integral_constant<bool, !std::is_same<U, void>::value>;

  static_assert(
      noexcept(std::declval<GrowthPolicy>().bucket_for_hash(std::size_t(0))),
      "GrowthPolicy::bucket_for_hash must be noexcept.");
  static_assert(noexcept(std::declval<GrowthPolicy>().clear()),
                "GrowthPolicy::clear must be noexcept.");

 public:
  template <bool IsConst>
  class hopscotch_iterator;

  using key_type = typename KeySelect::key_type;
  using value_type = ValueType;
  using size_type = std::size_t;
  using difference_type = std::ptrdiff_t;
  using hasher = Hash;
  using key_equal = KeyEqual;
  using allocator_type = Allocator;
  using reference = value_type&;
  using const_reference = const value_type&;
  using pointer = value_type*;
  using const_pointer = const value_type*;
  using iterator = hopscotch_iterator<false>;
  using const_iterator = hopscotch_iterator<true>;

 private:
  using hopscotch_bucket =
      collie::detail_hopscotch_hash::hopscotch_bucket<ValueType, NeighborhoodSize,
                                                   StoreHash>;
  using neighborhood_bitmap = typename hopscotch_bucket::neighborhood_bitmap;

  using buckets_allocator = typename std::allocator_traits<
      allocator_type>::template rebind_alloc<hopscotch_bucket>;
  using buckets_container_type =
      std::vector<hopscotch_bucket, buckets_allocator>;

  using overflow_container_type = OverflowContainer;

  static_assert(std::is_same<typename overflow_container_type::value_type,
                             ValueType>::value,
                "OverflowContainer should have ValueType as type.");

  static_assert(std::is_same<typename overflow_container_type::allocator_type,
                             Allocator>::value,
                "Invalid allocator, not the same type as the value_type.");

  using iterator_buckets = typename buckets_container_type::iterator;
  using const_iterator_buckets =
      typename buckets_container_type::const_iterator;

  using iterator_overflow = typename overflow_container_type::iterator;
  using const_iterator_overflow =
      typename overflow_container_type::const_iterator;

 public:
  /**
   * The `operator*()` and `operator->()` methods return a const reference and
   * const pointer respectively to the stored value type.
   *
   * In case of a map, to get a modifiable reference to the value associated to
   * a key (the `.second` in the stored pair), you have to call `value()`.
   */
  template <bool IsConst>
  class hopscotch_iterator {
    friend class hopscotch_hash;

   private:
    using iterator_bucket = typename std::conditional<
        IsConst, typename hopscotch_hash::const_iterator_buckets,
        typename hopscotch_hash::iterator_buckets>::type;
    using iterator_overflow = typename std::conditional<
        IsConst, typename hopscotch_hash::const_iterator_overflow,
        typename hopscotch_hash::iterator_overflow>::type;

    hopscotch_iterator(iterator_bucket buckets_iterator,
                       iterator_bucket buckets_end_iterator,
                       iterator_overflow overflow_iterator) noexcept
        : m_buckets_iterator(buckets_iterator),
          m_buckets_end_iterator(buckets_end_iterator),
          m_overflow_iterator(overflow_iterator) {}

   public:
    using iterator_category = std::forward_iterator_tag;
    using value_type = const typename hopscotch_hash::value_type;
    using difference_type = std::ptrdiff_t;
    using reference = value_type&;
    using pointer = value_type*;

    hopscotch_iterator() noexcept {}

    // Copy constructor from iterator to const_iterator.
    template <bool TIsConst = IsConst,
              typename std::enable_if<TIsConst>::type* = nullptr>
    hopscotch_iterator(const hopscotch_iterator<!TIsConst>& other) noexcept
        : m_buckets_iterator(other.m_buckets_iterator),
          m_buckets_end_iterator(other.m_buckets_end_iterator),
          m_overflow_iterator(other.m_overflow_iterator) {}

    hopscotch_iterator(const hopscotch_iterator& other) = default;
    hopscotch_iterator(hopscotch_iterator&& other) = default;
    hopscotch_iterator& operator=(const hopscotch_iterator& other) = default;
    hopscotch_iterator& operator=(hopscotch_iterator&& other) = default;

    const typename hopscotch_hash::key_type& key() const {
      if (m_buckets_iterator != m_buckets_end_iterator) {
        return KeySelect()(m_buckets_iterator->value());
      }

      return KeySelect()(*m_overflow_iterator);
    }

    template <
        class U = ValueSelect,
        typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
    typename std::conditional<IsConst, const typename U::value_type&,
                              typename U::value_type&>::type
    value() const {
      if (m_buckets_iterator != m_buckets_end_iterator) {
        return U()(m_buckets_iterator->value());
      }

      return U()(*m_overflow_iterator);
    }

    reference operator*() const {
      if (m_buckets_iterator != m_buckets_end_iterator) {
        return m_buckets_iterator->value();
      }

      return *m_overflow_iterator;
    }

    pointer operator->() const {
      if (m_buckets_iterator != m_buckets_end_iterator) {
        return std::addressof(m_buckets_iterator->value());
      }

      return std::addressof(*m_overflow_iterator);
    }

    hopscotch_iterator& operator++() {
      if (m_buckets_iterator == m_buckets_end_iterator) {
        ++m_overflow_iterator;
        return *this;
      }

      do {
        ++m_buckets_iterator;
      } while (m_buckets_iterator != m_buckets_end_iterator &&
               m_buckets_iterator->empty());

      return *this;
    }

    hopscotch_iterator operator++(int) {
      hopscotch_iterator tmp(*this);
      ++*this;

      return tmp;
    }

    friend bool operator==(const hopscotch_iterator& lhs,
                           const hopscotch_iterator& rhs) {
      return lhs.m_buckets_iterator == rhs.m_buckets_iterator &&
             lhs.m_overflow_iterator == rhs.m_overflow_iterator;
    }

    friend bool operator!=(const hopscotch_iterator& lhs,
                           const hopscotch_iterator& rhs) {
      return !(lhs == rhs);
    }

   private:
    iterator_bucket m_buckets_iterator;
    iterator_bucket m_buckets_end_iterator;
    iterator_overflow m_overflow_iterator;
  };

 public:
  template <
      class OC = OverflowContainer,
      typename std::enable_if<!has_key_compare<OC>::value>::type* = nullptr>
  hopscotch_hash() noexcept(
      hopscotch_hash::DEFAULT_INIT_BUCKETS_SIZE == 0 &&
      std::is_nothrow_default_constructible<Hash>::value &&
      std::is_nothrow_default_constructible<KeyEqual>::value &&
      std::is_nothrow_default_constructible<Allocator>::value &&
      (std::is_nothrow_constructible<GrowthPolicy, std::size_t&>::value ||
       hh::is_noexcept_on_zero_init<GrowthPolicy>::value))
      : hopscotch_hash(DEFAULT_INIT_BUCKETS_SIZE, Hash(), KeyEqual(),
                       Allocator(), DEFAULT_MAX_LOAD_FACTOR) {}

  template <
      class OC = OverflowContainer,
      typename std::enable_if<!has_key_compare<OC>::value>::type* = nullptr>
  hopscotch_hash(size_type bucket_count, const Hash& hash,
                 const KeyEqual& equal, const Allocator& alloc,
                 float max_load_factor)
      : Hash(hash),
        KeyEqual(equal),
        GrowthPolicy(bucket_count),
        m_buckets_data(alloc),
        m_overflow_elements(alloc),
        m_buckets(static_empty_bucket_ptr()),
        m_nb_elements(0) {
    if (bucket_count > max_bucket_count()) {
      TSL_HH_THROW_OR_TERMINATE(std::length_error,
                                "The map exceeds its maximum size.");
    }

    if (bucket_count > 0) {
      static_assert(NeighborhoodSize - 1 > 0, "");

      // Can't directly construct with the appropriate size in the initializer
      // as m_buckets_data(bucket_count, alloc) is not supported by GCC 4.8
      m_buckets_data.resize(bucket_count + NeighborhoodSize - 1);
      m_buckets = m_buckets_data.data();
    }

    this->max_load_factor(max_load_factor);

    // Check in the constructor instead of outside of a function to avoid
    // compilation issues when value_type is not complete.
    static_assert(std::is_nothrow_move_constructible<value_type>::value ||
                      std::is_copy_constructible<value_type>::value,
                  "value_type must be either copy constructible or nothrow "
                  "move constructible.");
  }

  template <
      class OC = OverflowContainer,
      typename std::enable_if<has_key_compare<OC>::value>::type* = nullptr>
  hopscotch_hash() noexcept(
      hopscotch_hash::DEFAULT_INIT_BUCKETS_SIZE == 0 &&
      std::is_nothrow_default_constructible<Hash>::value &&
      std::is_nothrow_default_constructible<KeyEqual>::value &&
      std::is_nothrow_default_constructible<Allocator>::value &&
      (std::is_nothrow_constructible<GrowthPolicy, std::size_t&>::value ||
       hh::is_noexcept_on_zero_init<GrowthPolicy>::value))
      : hopscotch_hash(DEFAULT_INIT_BUCKETS_SIZE, Hash(), KeyEqual(),
                       Allocator(), DEFAULT_MAX_LOAD_FACTOR,
                       typename OC::key_compare()) {}

  template <
      class OC = OverflowContainer,
      typename std::enable_if<has_key_compare<OC>::value>::type* = nullptr>
  hopscotch_hash(size_type bucket_count, const Hash& hash,
                 const KeyEqual& equal, const Allocator& alloc,
                 float max_load_factor, const typename OC::key_compare& comp)
      : Hash(hash),
        KeyEqual(equal),
        GrowthPolicy(bucket_count),
        m_buckets_data(alloc),
        m_overflow_elements(comp, alloc),
        m_buckets(static_empty_bucket_ptr()),
        m_nb_elements(0) {
    if (bucket_count > max_bucket_count()) {
      TSL_HH_THROW_OR_TERMINATE(std::length_error,
                                "The map exceeds its maximum size.");
    }

    if (bucket_count > 0) {
      static_assert(NeighborhoodSize - 1 > 0, "");

      // Can't directly construct with the appropriate size in the initializer
      // as m_buckets_data(bucket_count, alloc) is not supported by GCC 4.8
      m_buckets_data.resize(bucket_count + NeighborhoodSize - 1);
      m_buckets = m_buckets_data.data();
    }

    this->max_load_factor(max_load_factor);

    // Check in the constructor instead of outside of a function to avoid
    // compilation issues when value_type is not complete.
    static_assert(std::is_nothrow_move_constructible<value_type>::value ||
                      std::is_copy_constructible<value_type>::value,
                  "value_type must be either copy constructible or nothrow "
                  "move constructible.");
  }

  hopscotch_hash(const hopscotch_hash& other)
      : hopscotch_hash(other, other.get_allocator()) {}

  hopscotch_hash(const hopscotch_hash& other, const Allocator& alloc)
      : Hash(other),
        KeyEqual(other),
        GrowthPolicy(other),
        m_buckets_data(other.m_buckets_data, alloc),
        m_overflow_elements(other.m_overflow_elements),
        m_buckets(m_buckets_data.empty() ? static_empty_bucket_ptr()
                                         : m_buckets_data.data()),
        m_nb_elements(other.m_nb_elements),
        m_min_load_threshold_rehash(other.m_min_load_threshold_rehash),
        m_max_load_threshold_rehash(other.m_max_load_threshold_rehash),
        m_max_load_factor(other.m_max_load_factor) {}

  hopscotch_hash(hopscotch_hash&& other) noexcept(
      std::is_nothrow_move_constructible<Hash>::value&&
          std::is_nothrow_move_constructible<KeyEqual>::value&&
              std::is_nothrow_move_constructible<GrowthPolicy>::value&& std::
                  is_nothrow_move_constructible<buckets_container_type>::value&&
                      std::is_nothrow_move_constructible<
                          overflow_container_type>::value)
      : Hash(std::move(static_cast<Hash&>(other))),
        KeyEqual(std::move(static_cast<KeyEqual&>(other))),
        GrowthPolicy(std::move(static_cast<GrowthPolicy&>(other))),
        m_buckets_data(std::move(other.m_buckets_data)),
        m_overflow_elements(std::move(other.m_overflow_elements)),
        m_buckets(m_buckets_data.empty() ? static_empty_bucket_ptr()
                                         : m_buckets_data.data()),
        m_nb_elements(other.m_nb_elements),
        m_min_load_threshold_rehash(other.m_min_load_threshold_rehash),
        m_max_load_threshold_rehash(other.m_max_load_threshold_rehash),
        m_max_load_factor(other.m_max_load_factor) {
    other.GrowthPolicy::clear();
    other.m_buckets_data.clear();
    other.m_overflow_elements.clear();
    other.m_buckets = static_empty_bucket_ptr();
    other.m_nb_elements = 0;
    other.m_min_load_threshold_rehash = 0;
    other.m_max_load_threshold_rehash = 0;
  }

  hopscotch_hash& operator=(const hopscotch_hash& other) {
    if (&other != this) {
      Hash::operator=(other);
      KeyEqual::operator=(other);
      GrowthPolicy::operator=(other);

      m_buckets_data = other.m_buckets_data;
      m_overflow_elements = other.m_overflow_elements;
      m_buckets = m_buckets_data.empty() ? static_empty_bucket_ptr()
                                         : m_buckets_data.data();
      m_nb_elements = other.m_nb_elements;

      m_min_load_threshold_rehash = other.m_min_load_threshold_rehash;
      m_max_load_threshold_rehash = other.m_max_load_threshold_rehash;
      m_max_load_factor = other.m_max_load_factor;
    }

    return *this;
  }

  hopscotch_hash& operator=(hopscotch_hash&& other) noexcept(
      noexcept(other.swap(*this))) {
    other.swap(*this);
    other.clear();

    return *this;
  }

  allocator_type get_allocator() const {
    return m_buckets_data.get_allocator();
  }

  /*
   * Iterators
   */
  iterator begin() noexcept {
    auto begin = m_buckets_data.begin();
    while (begin != m_buckets_data.end() && begin->empty()) {
      ++begin;
    }

    return iterator(begin, m_buckets_data.end(), m_overflow_elements.begin());
  }

  const_iterator begin() const noexcept { return cbegin(); }

  const_iterator cbegin() const noexcept {
    auto begin = m_buckets_data.cbegin();
    while (begin != m_buckets_data.cend() && begin->empty()) {
      ++begin;
    }

    return const_iterator(begin, m_buckets_data.cend(),
                          m_overflow_elements.cbegin());
  }

  iterator end() noexcept {
    return iterator(m_buckets_data.end(), m_buckets_data.end(),
                    m_overflow_elements.end());
  }

  const_iterator end() const noexcept { return cend(); }

  const_iterator cend() const noexcept {
    return const_iterator(m_buckets_data.cend(), m_buckets_data.cend(),
                          m_overflow_elements.cend());
  }

  /*
   * Capacity
   */
  bool empty() const noexcept { return m_nb_elements == 0; }

  size_type size() const noexcept { return m_nb_elements; }

  size_type max_size() const noexcept { return m_buckets_data.max_size(); }

  /*
   * Modifiers
   */
  void clear() noexcept {
    for (auto& bucket : m_buckets_data) {
      bucket.clear();
    }

    m_overflow_elements.clear();
    m_nb_elements = 0;
  }

  std::pair<iterator, bool> insert(const value_type& value) {
    return insert_impl(value);
  }

  template <class P, typename std::enable_if<std::is_constructible<
                         value_type, P&&>::value>::type* = nullptr>
  std::pair<iterator, bool> insert(P&& value) {
    return insert_impl(std::forward<P>(value));
  }

  std::pair<iterator, bool> insert(value_type&& value) {
    return insert_impl(std::move(value));
  }

  iterator insert(const_iterator hint, const value_type& value) {
    if (hint != cend() &&
        compare_keys(KeySelect()(*hint), KeySelect()(value))) {
      return mutable_iterator(hint);
    }

    return insert(value).first;
  }

  template <class P, typename std::enable_if<std::is_constructible<
                         value_type, P&&>::value>::type* = nullptr>
  iterator insert(const_iterator hint, P&& value) {
    if (hint != cend() &&
        compare_keys(KeySelect()(*hint), KeySelect()(value))) {
      return mutable_iterator(hint);
    }

    return insert(std::forward<P>(value)).first;
  }

  iterator insert(const_iterator hint, value_type&& value) {
    if (hint != cend() &&
        compare_keys(KeySelect()(*hint), KeySelect()(value))) {
      return mutable_iterator(hint);
    }

    return insert(std::move(value)).first;
  }

  template <class InputIt>
  void insert(InputIt first, InputIt last) {
    if (std::is_base_of<
            std::forward_iterator_tag,
            typename std::iterator_traits<InputIt>::iterator_category>::value) {
      const auto nb_elements_insert = std::distance(first, last);
      const std::size_t nb_elements_in_buckets =
          m_nb_elements - m_overflow_elements.size();
      const std::size_t nb_free_buckets =
          m_max_load_threshold_rehash - nb_elements_in_buckets;
      tsl_hh_assert(m_nb_elements >= m_overflow_elements.size());
      tsl_hh_assert(m_max_load_threshold_rehash >= nb_elements_in_buckets);

      if (nb_elements_insert > 0 &&
          nb_free_buckets < std::size_t(nb_elements_insert)) {
        reserve(nb_elements_in_buckets + std::size_t(nb_elements_insert));
      }
    }

    for (; first != last; ++first) {
      insert(*first);
    }
  }

  template <class M>
  std::pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj) {
    return insert_or_assign_impl(k, std::forward<M>(obj));
  }

  template <class M>
  std::pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj) {
    return insert_or_assign_impl(std::move(k), std::forward<M>(obj));
  }

  template <class K, class M>
  std::pair<iterator, bool> insert_or_assign(K&& k, M&& obj) {
    return insert_or_assign_impl(std::forward<K>(k), std::forward<M>(obj));
  }

  template <class M>
  iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj) {
    if (hint != cend() && compare_keys(KeySelect()(*hint), k)) {
      auto it = mutable_iterator(hint);
      it.value() = std::forward<M>(obj);

      return it;
    }

    return insert_or_assign(k, std::forward<M>(obj)).first;
  }

  template <class M>
  iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj) {
    if (hint != cend() && compare_keys(KeySelect()(*hint), k)) {
      auto it = mutable_iterator(hint);
      it.value() = std::forward<M>(obj);

      return it;
    }

    return insert_or_assign(std::move(k), std::forward<M>(obj)).first;
  }

  template <class K, class M>
  iterator insert_or_assign(const_iterator hint, K&& k, M&& obj) {
    if (hint != cend() && compare_keys(KeySelect()(*hint), k)) {
      auto it = mutable_iterator(hint);
      it.value() = std::forward<M>(obj);

      return it;
    }

    return insert_or_assign(std::forward<K>(k), std::forward<M>(obj)).first;
  }

  template <class... Args>
  std::pair<iterator, bool> emplace(Args&&... args) {
    return insert(value_type(std::forward<Args>(args)...));
  }

  template <class... Args>
  iterator emplace_hint(const_iterator hint, Args&&... args) {
    return insert(hint, value_type(std::forward<Args>(args)...));
  }

  template <class... Args>
  std::pair<iterator, bool> try_emplace(const key_type& k, Args&&... args) {
    return try_emplace_impl(k, std::forward<Args>(args)...);
  }

  template <class... Args>
  std::pair<iterator, bool> try_emplace(key_type&& k, Args&&... args) {
    return try_emplace_impl(std::move(k), std::forward<Args>(args)...);
  }

  template <class K, class... Args>
  std::pair<iterator, bool> try_emplace(K&& k, Args&&... args) {
    return try_emplace_impl(std::forward<K>(k), std::forward<Args>(args)...);
  }

  template <class... Args>
  iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args) {
    if (hint != cend() && compare_keys(KeySelect()(*hint), k)) {
      return mutable_iterator(hint);
    }

    return try_emplace(k, std::forward<Args>(args)...).first;
  }

  template <class... Args>
  iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args) {
    if (hint != cend() && compare_keys(KeySelect()(*hint), k)) {
      return mutable_iterator(hint);
    }

    return try_emplace(std::move(k), std::forward<Args>(args)...).first;
  }

  template <class K, class... Args>
  iterator try_emplace(const_iterator hint, K&& k, Args&&... args) {
    if (hint != cend() && compare_keys(KeySelect()(*hint), k)) {
      return mutable_iterator(hint);
    }

    return try_emplace(std::forward<K>(k), std::forward<Args>(args)...).first;
  }

  /**
   * Here to avoid `template<class K> size_type erase(const K& key)` being used
   * when we use an iterator instead of a const_iterator.
   */
  iterator erase(iterator pos) { return erase(const_iterator(pos)); }

  iterator erase(const_iterator pos) {
    const std::size_t ibucket_for_hash = bucket_for_hash(hash_key(pos.key()));

    if (pos.m_buckets_iterator != pos.m_buckets_end_iterator) {
      auto it_bucket =
          m_buckets_data.begin() +
          std::distance(m_buckets_data.cbegin(), pos.m_buckets_iterator);
      erase_from_bucket(*it_bucket, ibucket_for_hash);

      return ++iterator(it_bucket, m_buckets_data.end(),
                        m_overflow_elements.begin());
    } else {
      auto it_next_overflow =
          erase_from_overflow(pos.m_overflow_iterator, ibucket_for_hash);
      return iterator(m_buckets_data.end(), m_buckets_data.end(),
                      it_next_overflow);
    }
  }

  iterator erase(const_iterator first, const_iterator last) {
    if (first == last) {
      return mutable_iterator(first);
    }

    auto to_delete = erase(first);
    while (to_delete != last) {
      to_delete = erase(to_delete);
    }

    return to_delete;
  }

  template <class K>
  size_type erase(const K& key) {
    return erase(key, hash_key(key));
  }

  template <class K>
  size_type erase(const K& key, std::size_t hash) {
    const std::size_t ibucket_for_hash = bucket_for_hash(hash);

    hopscotch_bucket* bucket_found =
        find_in_buckets(key, hash, m_buckets + ibucket_for_hash);
    if (bucket_found != nullptr) {
      erase_from_bucket(*bucket_found, ibucket_for_hash);

      return 1;
    }

    if (m_buckets[ibucket_for_hash].has_overflow()) {
      auto it_overflow = find_in_overflow(key);
      if (it_overflow != m_overflow_elements.end()) {
        erase_from_overflow(it_overflow, ibucket_for_hash);

        return 1;
      }
    }

    return 0;
  }

  void swap(hopscotch_hash& other) noexcept(
      std::is_nothrow_swappable<Hash>::value&& std::is_nothrow_swappable<
          KeyEqual>::value&& std::is_nothrow_swappable<GrowthPolicy>::value&&
          std::is_nothrow_swappable<buckets_container_type>::value&&
              std::is_nothrow_swappable<overflow_container_type>::value) {
    using std::swap;

    swap(static_cast<Hash&>(*this), static_cast<Hash&>(other));
    swap(static_cast<KeyEqual&>(*this), static_cast<KeyEqual&>(other));
    swap(static_cast<GrowthPolicy&>(*this), static_cast<GrowthPolicy&>(other));
    swap(m_buckets_data, other.m_buckets_data);
    swap(m_overflow_elements, other.m_overflow_elements);
    swap(m_buckets, other.m_buckets);
    swap(m_nb_elements, other.m_nb_elements);
    swap(m_min_load_threshold_rehash, other.m_min_load_threshold_rehash);
    swap(m_max_load_threshold_rehash, other.m_max_load_threshold_rehash);
    swap(m_max_load_factor, other.m_max_load_factor);
  }

  /*
   * Lookup
   */
  template <class K, class U = ValueSelect,
            typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
  typename U::value_type& at(const K& key) {
    return at(key, hash_key(key));
  }

  template <class K, class U = ValueSelect,
            typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
  typename U::value_type& at(const K& key, std::size_t hash) {
    return const_cast<typename U::value_type&>(
        static_cast<const hopscotch_hash*>(this)->at(key, hash));
  }

  template <class K, class U = ValueSelect,
            typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
  const typename U::value_type& at(const K& key) const {
    return at(key, hash_key(key));
  }

  template <class K, class U = ValueSelect,
            typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
  const typename U::value_type& at(const K& key, std::size_t hash) const {
    using T = typename U::value_type;

    const T* value =
        find_value_impl(key, hash, m_buckets + bucket_for_hash(hash));
    if (value == nullptr) {
      TSL_HH_THROW_OR_TERMINATE(std::out_of_range, "Couldn't find key.");
    } else {
      return *value;
    }
  }

  template <class K, class U = ValueSelect,
            typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
  typename U::value_type& operator[](K&& key) {
    using T = typename U::value_type;

    const std::size_t hash = hash_key(key);
    const std::size_t ibucket_for_hash = bucket_for_hash(hash);

    T* value = find_value_impl(key, hash, m_buckets + ibucket_for_hash);
    if (value != nullptr) {
      return *value;
    } else {
      return insert_value(ibucket_for_hash, hash, std::piecewise_construct,
                          std::forward_as_tuple(std::forward<K>(key)),
                          std::forward_as_tuple())
          .first.value();
    }
  }

  template <class K>
  size_type count(const K& key) const {
    return count(key, hash_key(key));
  }

  template <class K>
  size_type count(const K& key, std::size_t hash) const {
    return count_impl(key, hash, m_buckets + bucket_for_hash(hash));
  }

  template <class K>
  iterator find(const K& key) {
    return find(key, hash_key(key));
  }

  template <class K>
  iterator find(const K& key, std::size_t hash) {
    return find_impl(key, hash, m_buckets + bucket_for_hash(hash));
  }

  template <class K>
  const_iterator find(const K& key) const {
    return find(key, hash_key(key));
  }

  template <class K>
  const_iterator find(const K& key, std::size_t hash) const {
    return find_impl(key, hash, m_buckets + bucket_for_hash(hash));
  }

  template <class K>
  bool contains(const K& key) const {
    return contains(key, hash_key(key));
  }

  template <class K>
  bool contains(const K& key, std::size_t hash) const {
    return count(key, hash) != 0;
  }

  template <class K>
  std::pair<iterator, iterator> equal_range(const K& key) {
    return equal_range(key, hash_key(key));
  }

  template <class K>
  std::pair<iterator, iterator> equal_range(const K& key, std::size_t hash) {
    iterator it = find(key, hash);
    return std::make_pair(it, (it == end()) ? it : std::next(it));
  }

  template <class K>
  std::pair<const_iterator, const_iterator> equal_range(const K& key) const {
    return equal_range(key, hash_key(key));
  }

  template <class K>
  std::pair<const_iterator, const_iterator> equal_range(
      const K& key, std::size_t hash) const {
    const_iterator it = find(key, hash);
    return std::make_pair(it, (it == cend()) ? it : std::next(it));
  }

  /*
   * Bucket interface
   */
  size_type bucket_count() const {
    /*
     * So that the last bucket can have NeighborhoodSize neighbors, the size of
     * the bucket array is a little bigger than the real number of buckets when
     * not empty. We could use some of the buckets at the beginning, but it is
     * faster this way as we avoid extra checks.
     */
    if (m_buckets_data.empty()) {
      return 0;
    }

    return m_buckets_data.size() - NeighborhoodSize + 1;
  }

  size_type max_bucket_count() const {
    const std::size_t max_bucket_count =
        std::min(GrowthPolicy::max_bucket_count(), m_buckets_data.max_size());
    return max_bucket_count - NeighborhoodSize + 1;
  }

  /*
   *  Hash policy
   */
  float load_factor() const {
    if (bucket_count() == 0) {
      return 0;
    }

    return float(m_nb_elements) / float(bucket_count());
  }

  float max_load_factor() const { return m_max_load_factor; }

  void max_load_factor(float ml) {
    m_max_load_factor = std::max(0.1f, std::min(ml, 0.95f));
    m_min_load_threshold_rehash =
        size_type(float(bucket_count()) * MIN_LOAD_FACTOR_FOR_REHASH);
    m_max_load_threshold_rehash =
        size_type(float(bucket_count()) * m_max_load_factor);
  }

  void rehash(size_type count_) {
    count_ = std::max(count_,
                      size_type(std::ceil(float(size()) / max_load_factor())));
    rehash_impl(count_);
  }

  void reserve(size_type count_) {
    rehash(size_type(std::ceil(float(count_) / max_load_factor())));
  }

  /*
   * Observers
   */
  hasher hash_function() const { return static_cast<const Hash&>(*this); }

  key_equal key_eq() const { return static_cast<const KeyEqual&>(*this); }

  /*
   * Other
   */
  iterator mutable_iterator(const_iterator pos) {
    if (pos.m_buckets_iterator != pos.m_buckets_end_iterator) {
      // Get a non-const iterator
      auto it = m_buckets_data.begin() +
                std::distance(m_buckets_data.cbegin(), pos.m_buckets_iterator);
      return iterator(it, m_buckets_data.end(), m_overflow_elements.begin());
    } else {
      // Get a non-const iterator
      auto it = mutable_overflow_iterator(pos.m_overflow_iterator);
      return iterator(m_buckets_data.end(), m_buckets_data.end(), it);
    }
  }

  size_type overflow_size() const noexcept {
    return m_overflow_elements.size();
  }

  template <class U = OverflowContainer,
            typename std::enable_if<has_key_compare<U>::value>::type* = nullptr>
  typename U::key_compare key_comp() const {
    return m_overflow_elements.key_comp();
  }

 private:
  template <class K>
  std::size_t hash_key(const K& key) const {
    return Hash::operator()(key);
  }

  template <class K1, class K2>
  bool compare_keys(const K1& key1, const K2& key2) const {
    return KeyEqual::operator()(key1, key2);
  }

  std::size_t bucket_for_hash(std::size_t hash) const {
    const std::size_t bucket = GrowthPolicy::bucket_for_hash(hash);
    tsl_hh_assert(bucket < m_buckets_data.size() ||
                  (bucket == 0 && m_buckets_data.empty()));

    return bucket;
  }

  template <typename U = value_type,
            typename std::enable_if<
                std::is_nothrow_move_constructible<U>::value>::type* = nullptr>
  void rehash_impl(size_type count_) {
    hopscotch_hash new_map = new_hopscotch_hash(count_);

    if (!m_overflow_elements.empty()) {
      new_map.m_overflow_elements.swap(m_overflow_elements);
      new_map.m_nb_elements += new_map.m_overflow_elements.size();

      for (const value_type& value : new_map.m_overflow_elements) {
        const std::size_t ibucket_for_hash =
            new_map.bucket_for_hash(new_map.hash_key(KeySelect()(value)));
        new_map.m_buckets[ibucket_for_hash].set_overflow(true);
      }
    }

#ifndef TSL_HH_NO_EXCEPTIONS
    try {
#endif
      const bool use_stored_hash =
          USE_STORED_HASH_ON_REHASH(new_map.bucket_count());
      for (auto it_bucket = m_buckets_data.begin();
           it_bucket != m_buckets_data.end(); ++it_bucket) {
        if (it_bucket->empty()) {
          continue;
        }

        const std::size_t hash =
            use_stored_hash ? it_bucket->truncated_bucket_hash()
                            : new_map.hash_key(KeySelect()(it_bucket->value()));
        const std::size_t ibucket_for_hash = new_map.bucket_for_hash(hash);

        new_map.insert_value(ibucket_for_hash, hash,
                             std::move(it_bucket->value()));

        erase_from_bucket(*it_bucket, bucket_for_hash(hash));
      }
#ifndef TSL_HH_NO_EXCEPTIONS
    }
    /*
     * The call to insert_value may throw an exception if an element is added to
     * the overflow list and the memory allocation fails. Rollback the elements
     * in this case.
     */
    catch (...) {
      m_overflow_elements.swap(new_map.m_overflow_elements);

      const bool use_stored_hash =
          USE_STORED_HASH_ON_REHASH(new_map.bucket_count());
      for (auto it_bucket = new_map.m_buckets_data.begin();
           it_bucket != new_map.m_buckets_data.end(); ++it_bucket) {
        if (it_bucket->empty()) {
          continue;
        }

        const std::size_t hash =
            use_stored_hash ? it_bucket->truncated_bucket_hash()
                            : hash_key(KeySelect()(it_bucket->value()));
        const std::size_t ibucket_for_hash = bucket_for_hash(hash);

        // The elements we insert were not in the overflow list before the
        // switch. They will not be go in the overflow list if we rollback the
        // switch.
        insert_value(ibucket_for_hash, hash, std::move(it_bucket->value()));
      }

      throw;
    }
#endif

    new_map.swap(*this);
  }

  template <typename U = value_type,
            typename std::enable_if<
                std::is_copy_constructible<U>::value &&
                !std::is_nothrow_move_constructible<U>::value>::type* = nullptr>
  void rehash_impl(size_type count_) {
    hopscotch_hash new_map = new_hopscotch_hash(count_);

    const bool use_stored_hash =
        USE_STORED_HASH_ON_REHASH(new_map.bucket_count());
    for (const hopscotch_bucket& bucket : m_buckets_data) {
      if (bucket.empty()) {
        continue;
      }

      const std::size_t hash =
          use_stored_hash ? bucket.truncated_bucket_hash()
                          : new_map.hash_key(KeySelect()(bucket.value()));
      const std::size_t ibucket_for_hash = new_map.bucket_for_hash(hash);

      new_map.insert_value(ibucket_for_hash, hash, bucket.value());
    }

    for (const value_type& value : m_overflow_elements) {
      const std::size_t hash = new_map.hash_key(KeySelect()(value));
      const std::size_t ibucket_for_hash = new_map.bucket_for_hash(hash);

      new_map.insert_value(ibucket_for_hash, hash, value);
    }

    new_map.swap(*this);
  }

  iterator_overflow mutable_overflow_iterator(const_iterator_overflow it) {
    return m_overflow_elements.erase(it, it);
  }

  // iterator is in overflow list
  iterator_overflow erase_from_overflow(const_iterator_overflow pos,
                                        std::size_t ibucket_for_hash) {
    auto it_next = m_overflow_elements.erase(pos);
    m_nb_elements--;

    // Check if we can remove the overflow flag
    tsl_hh_assert(m_buckets[ibucket_for_hash].has_overflow());
    for (const value_type& value : m_overflow_elements) {
      const std::size_t bucket_for_value =
          bucket_for_hash(hash_key(KeySelect()(value)));
      if (bucket_for_value == ibucket_for_hash) {
        return it_next;
      }
    }

    m_buckets[ibucket_for_hash].set_overflow(false);
    return it_next;
  }

  /**
   * bucket_for_value is the bucket in which the value is.
   * ibucket_for_hash is the bucket where the value belongs.
   */
  void erase_from_bucket(hopscotch_bucket& bucket_for_value,
                         std::size_t ibucket_for_hash) noexcept {
    const std::size_t ibucket_for_value =
        std::distance(m_buckets_data.data(), &bucket_for_value);
    tsl_hh_assert(ibucket_for_value >= ibucket_for_hash);

    bucket_for_value.remove_value();
    m_buckets[ibucket_for_hash].toggle_neighbor_presence(ibucket_for_value -
                                                         ibucket_for_hash);
    m_nb_elements--;
  }

  template <class K, class M>
  std::pair<iterator, bool> insert_or_assign_impl(K&& key, M&& obj) {
    auto it = try_emplace_impl(std::forward<K>(key), std::forward<M>(obj));
    if (!it.second) {
      it.first.value() = std::forward<M>(obj);
    }

    return it;
  }

  template <typename P, class... Args>
  std::pair<iterator, bool> try_emplace_impl(P&& key, Args&&... args_value) {
    const std::size_t hash = hash_key(key);
    const std::size_t ibucket_for_hash = bucket_for_hash(hash);

    // Check if already presents
    auto it_find = find_impl(key, hash, m_buckets + ibucket_for_hash);
    if (it_find != end()) {
      return std::make_pair(it_find, false);
    }

    return insert_value(
        ibucket_for_hash, hash, std::piecewise_construct,
        std::forward_as_tuple(std::forward<P>(key)),
        std::forward_as_tuple(std::forward<Args>(args_value)...));
  }

  template <typename P>
  std::pair<iterator, bool> insert_impl(P&& value) {
    const std::size_t hash = hash_key(KeySelect()(value));
    const std::size_t ibucket_for_hash = bucket_for_hash(hash);

    // Check if already presents
    auto it_find =
        find_impl(KeySelect()(value), hash, m_buckets + ibucket_for_hash);
    if (it_find != end()) {
      return std::make_pair(it_find, false);
    }

    return insert_value(ibucket_for_hash, hash, std::forward<P>(value));
  }

  template <typename... Args>
  std::pair<iterator, bool> insert_value(std::size_t ibucket_for_hash,
                                         std::size_t hash,
                                         Args&&... value_type_args) {
    if ((m_nb_elements - m_overflow_elements.size()) >=
        m_max_load_threshold_rehash) {
      rehash(GrowthPolicy::next_bucket_count());
      ibucket_for_hash = bucket_for_hash(hash);
    }

    std::size_t ibucket_empty = find_empty_bucket(ibucket_for_hash);
    if (ibucket_empty < m_buckets_data.size()) {
      do {
        tsl_hh_assert(ibucket_empty >= ibucket_for_hash);

        // Empty bucket is in range of NeighborhoodSize, use it
        if (ibucket_empty - ibucket_for_hash < NeighborhoodSize) {
          auto it = insert_in_bucket(ibucket_empty, ibucket_for_hash, hash,
                                     std::forward<Args>(value_type_args)...);
          return std::make_pair(
              iterator(it, m_buckets_data.end(), m_overflow_elements.begin()),
              true);
        }
      }
      // else, try to swap values to get a closer empty bucket
      while (swap_empty_bucket_closer(ibucket_empty));
    }

    // Load factor is too low or a rehash will not change the neighborhood, put
    // the value in overflow list
    if (size() < m_min_load_threshold_rehash ||
        !will_neighborhood_change_on_rehash(ibucket_for_hash)) {
      auto it = insert_in_overflow(ibucket_for_hash,
                                   std::forward<Args>(value_type_args)...);
      return std::make_pair(
          iterator(m_buckets_data.end(), m_buckets_data.end(), it), true);
    }

    rehash(GrowthPolicy::next_bucket_count());
    ibucket_for_hash = bucket_for_hash(hash);

    return insert_value(ibucket_for_hash, hash,
                        std::forward<Args>(value_type_args)...);
  }

  /*
   * Return true if a rehash will change the position of a key-value in the
   * neighborhood of ibucket_neighborhood_check. In this case a rehash is needed
   * instead of puting the value in overflow list.
   */
  bool will_neighborhood_change_on_rehash(
      size_t ibucket_neighborhood_check) const {
    std::size_t expand_bucket_count = GrowthPolicy::next_bucket_count();
    GrowthPolicy expand_growth_policy(expand_bucket_count);

    const bool use_stored_hash = USE_STORED_HASH_ON_REHASH(expand_bucket_count);
    for (size_t ibucket = ibucket_neighborhood_check;
         ibucket < m_buckets_data.size() &&
         (ibucket - ibucket_neighborhood_check) < NeighborhoodSize;
         ++ibucket) {
      tsl_hh_assert(!m_buckets[ibucket].empty());

      const size_t hash =
          use_stored_hash ? m_buckets[ibucket].truncated_bucket_hash()
                          : hash_key(KeySelect()(m_buckets[ibucket].value()));
      if (bucket_for_hash(hash) != expand_growth_policy.bucket_for_hash(hash)) {
        return true;
      }
    }

    return false;
  }

  /*
   * Return the index of an empty bucket in m_buckets_data.
   * If none, the returned index equals m_buckets_data.size()
   */
  std::size_t find_empty_bucket(std::size_t ibucket_start) const {
    const std::size_t limit = std::min(
        ibucket_start + MAX_PROBES_FOR_EMPTY_BUCKET, m_buckets_data.size());
    for (; ibucket_start < limit; ibucket_start++) {
      if (m_buckets[ibucket_start].empty()) {
        return ibucket_start;
      }
    }

    return m_buckets_data.size();
  }

  /*
   * Insert value in ibucket_empty where value originally belongs to
   * ibucket_for_hash
   *
   * Return bucket iterator to ibucket_empty
   */
  template <typename... Args>
  iterator_buckets insert_in_bucket(std::size_t ibucket_empty,
                                    std::size_t ibucket_for_hash,
                                    std::size_t hash,
                                    Args&&... value_type_args) {
    tsl_hh_assert(ibucket_empty >= ibucket_for_hash);
    tsl_hh_assert(m_buckets[ibucket_empty].empty());
    m_buckets[ibucket_empty].set_value_of_empty_bucket(
        hopscotch_bucket::truncate_hash(hash),
        std::forward<Args>(value_type_args)...);

    tsl_hh_assert(!m_buckets[ibucket_for_hash].empty());
    m_buckets[ibucket_for_hash].toggle_neighbor_presence(ibucket_empty -
                                                         ibucket_for_hash);
    m_nb_elements++;

    return m_buckets_data.begin() + ibucket_empty;
  }

  template <
      class... Args, class U = OverflowContainer,
      typename std::enable_if<!has_key_compare<U>::value>::type* = nullptr>
  iterator_overflow insert_in_overflow(std::size_t ibucket_for_hash,
                                       Args&&... value_type_args) {
    auto it = m_overflow_elements.emplace(
        m_overflow_elements.end(), std::forward<Args>(value_type_args)...);

    m_buckets[ibucket_for_hash].set_overflow(true);
    m_nb_elements++;

    return it;
  }

  template <class... Args, class U = OverflowContainer,
            typename std::enable_if<has_key_compare<U>::value>::type* = nullptr>
  iterator_overflow insert_in_overflow(std::size_t ibucket_for_hash,
                                       Args&&... value_type_args) {
    auto it =
        m_overflow_elements.emplace(std::forward<Args>(value_type_args)...)
            .first;

    m_buckets[ibucket_for_hash].set_overflow(true);
    m_nb_elements++;

    return it;
  }

  /*
   * Try to swap the bucket ibucket_empty_in_out with a bucket preceding it
   * while keeping the neighborhood conditions correct.
   *
   * If a swap was possible, the position of ibucket_empty_in_out will be closer
   * to 0 and true will re returned.
   */
  bool swap_empty_bucket_closer(std::size_t& ibucket_empty_in_out) {
    tsl_hh_assert(ibucket_empty_in_out >= NeighborhoodSize);
    const std::size_t neighborhood_start =
        ibucket_empty_in_out - NeighborhoodSize + 1;

    for (std::size_t to_check = neighborhood_start;
         to_check < ibucket_empty_in_out; to_check++) {
      neighborhood_bitmap neighborhood_infos =
          m_buckets[to_check].neighborhood_infos();
      std::size_t to_swap = to_check;

      while (neighborhood_infos != 0 && to_swap < ibucket_empty_in_out) {
        if ((neighborhood_infos & 1) == 1) {
          tsl_hh_assert(m_buckets[ibucket_empty_in_out].empty());
          tsl_hh_assert(!m_buckets[to_swap].empty());

          m_buckets[to_swap].swap_value_into_empty_bucket(
              m_buckets[ibucket_empty_in_out]);

          tsl_hh_assert(!m_buckets[to_check].check_neighbor_presence(
              ibucket_empty_in_out - to_check));
          tsl_hh_assert(
              m_buckets[to_check].check_neighbor_presence(to_swap - to_check));

          m_buckets[to_check].toggle_neighbor_presence(ibucket_empty_in_out -
                                                       to_check);
          m_buckets[to_check].toggle_neighbor_presence(to_swap - to_check);

          ibucket_empty_in_out = to_swap;

          return true;
        }

        to_swap++;
        neighborhood_infos = neighborhood_bitmap(neighborhood_infos >> 1);
      }
    }

    return false;
  }

  template <class K, class U = ValueSelect,
            typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
  typename U::value_type* find_value_impl(const K& key, std::size_t hash,
                                          hopscotch_bucket* bucket_for_hash) {
    return const_cast<typename U::value_type*>(
        static_cast<const hopscotch_hash*>(this)->find_value_impl(
            key, hash, bucket_for_hash));
  }

  /*
   * Avoid the creation of an iterator to just get the value for operator[] and
   * at() in maps. Faster this way.
   *
   * Return null if no value for the key (TODO use std::optional when
   * available).
   */
  template <class K, class U = ValueSelect,
            typename std::enable_if<has_mapped_type<U>::value>::type* = nullptr>
  const typename U::value_type* find_value_impl(
      const K& key, std::size_t hash,
      const hopscotch_bucket* bucket_for_hash) const {
    const hopscotch_bucket* bucket_found =
        find_in_buckets(key, hash, bucket_for_hash);
    if (bucket_found != nullptr) {
      return std::addressof(ValueSelect()(bucket_found->value()));
    }

    if (bucket_for_hash->has_overflow()) {
      auto it_overflow = find_in_overflow(key);
      if (it_overflow != m_overflow_elements.end()) {
        return std::addressof(ValueSelect()(*it_overflow));
      }
    }

    return nullptr;
  }

  template <class K>
  size_type count_impl(const K& key, std::size_t hash,
                       const hopscotch_bucket* bucket_for_hash) const {
    if (find_in_buckets(key, hash, bucket_for_hash) != nullptr) {
      return 1;
    } else if (bucket_for_hash->has_overflow() &&
               find_in_overflow(key) != m_overflow_elements.cend()) {
      return 1;
    } else {
      return 0;
    }
  }

  template <class K>
  iterator find_impl(const K& key, std::size_t hash,
                     hopscotch_bucket* bucket_for_hash) {
    hopscotch_bucket* bucket_found =
        find_in_buckets(key, hash, bucket_for_hash);
    if (bucket_found != nullptr) {
      return iterator(m_buckets_data.begin() +
                          std::distance(m_buckets_data.data(), bucket_found),
                      m_buckets_data.end(), m_overflow_elements.begin());
    }

    if (!bucket_for_hash->has_overflow()) {
      return end();
    }

    return iterator(m_buckets_data.end(), m_buckets_data.end(),
                    find_in_overflow(key));
  }

  template <class K>
  const_iterator find_impl(const K& key, std::size_t hash,
                           const hopscotch_bucket* bucket_for_hash) const {
    const hopscotch_bucket* bucket_found =
        find_in_buckets(key, hash, bucket_for_hash);
    if (bucket_found != nullptr) {
      return const_iterator(
          m_buckets_data.cbegin() +
              std::distance(m_buckets_data.data(), bucket_found),
          m_buckets_data.cend(), m_overflow_elements.cbegin());
    }

    if (!bucket_for_hash->has_overflow()) {
      return cend();
    }

    return const_iterator(m_buckets_data.cend(), m_buckets_data.cend(),
                          find_in_overflow(key));
  }

  template <class K>
  hopscotch_bucket* find_in_buckets(const K& key, std::size_t hash,
                                    hopscotch_bucket* bucket_for_hash) {
    const hopscotch_bucket* bucket_found =
        static_cast<const hopscotch_hash*>(this)->find_in_buckets(
            key, hash, bucket_for_hash);
    return const_cast<hopscotch_bucket*>(bucket_found);
  }

  /**
   * Return a pointer to the bucket which has the value, nullptr otherwise.
   */
  template <class K>
  const hopscotch_bucket* find_in_buckets(
      const K& key, std::size_t hash,
      const hopscotch_bucket* bucket_for_hash) const {
    (void)hash;  // Avoid warning of unused variable when StoreHash is false;

    // TODO Try to optimize the function.
    // I tried to use ffs and  __builtin_ffs functions but I could not reduce
    // the time the function takes with -march=native

    neighborhood_bitmap neighborhood_infos =
        bucket_for_hash->neighborhood_infos();
    while (neighborhood_infos != 0) {
      if ((neighborhood_infos & 1) == 1) {
        // Check StoreHash before calling bucket_hash_equal. Functionally it
        // doesn't change anythin. If StoreHash is false, bucket_hash_equal is a
        // no-op. Avoiding the call is there to help GCC optimizes `hash`
        // parameter away, it seems to not be able to do without this hint.
        if ((!StoreHash || bucket_for_hash->bucket_hash_equal(hash)) &&
            compare_keys(KeySelect()(bucket_for_hash->value()), key)) {
          return bucket_for_hash;
        }
      }

      ++bucket_for_hash;
      neighborhood_infos = neighborhood_bitmap(neighborhood_infos >> 1);
    }

    return nullptr;
  }

  template <
      class K, class U = OverflowContainer,
      typename std::enable_if<!has_key_compare<U>::value>::type* = nullptr>
  iterator_overflow find_in_overflow(const K& key) {
    return std::find_if(m_overflow_elements.begin(), m_overflow_elements.end(),
                        [&](const value_type& value) {
                          return compare_keys(key, KeySelect()(value));
                        });
  }

  template <
      class K, class U = OverflowContainer,
      typename std::enable_if<!has_key_compare<U>::value>::type* = nullptr>
  const_iterator_overflow find_in_overflow(const K& key) const {
    return std::find_if(m_overflow_elements.cbegin(),
                        m_overflow_elements.cend(),
                        [&](const value_type& value) {
                          return compare_keys(key, KeySelect()(value));
                        });
  }

  template <class K, class U = OverflowContainer,
            typename std::enable_if<has_key_compare<U>::value>::type* = nullptr>
  iterator_overflow find_in_overflow(const K& key) {
    return m_overflow_elements.find(key);
  }

  template <class K, class U = OverflowContainer,
            typename std::enable_if<has_key_compare<U>::value>::type* = nullptr>
  const_iterator_overflow find_in_overflow(const K& key) const {
    return m_overflow_elements.find(key);
  }

  template <
      class U = OverflowContainer,
      typename std::enable_if<!has_key_compare<U>::value>::type* = nullptr>
  hopscotch_hash new_hopscotch_hash(size_type bucket_count) {
    return hopscotch_hash(bucket_count, static_cast<Hash&>(*this),
                          static_cast<KeyEqual&>(*this), get_allocator(),
                          m_max_load_factor);
  }

  template <class U = OverflowContainer,
            typename std::enable_if<has_key_compare<U>::value>::type* = nullptr>
  hopscotch_hash new_hopscotch_hash(size_type bucket_count) {
    return hopscotch_hash(bucket_count, static_cast<Hash&>(*this),
                          static_cast<KeyEqual&>(*this), get_allocator(),
                          m_max_load_factor, m_overflow_elements.key_comp());
  }

 public:
  static const size_type DEFAULT_INIT_BUCKETS_SIZE = 0;
  static constexpr float DEFAULT_MAX_LOAD_FACTOR =
      (NeighborhoodSize <= 30) ? 0.8f : 0.9f;

 private:
  static const std::size_t MAX_PROBES_FOR_EMPTY_BUCKET = 12 * NeighborhoodSize;
  static constexpr float MIN_LOAD_FACTOR_FOR_REHASH = 0.1f;

  /**
   * We can only use the hash on rehash if the size of the hash type is the same
   * as the stored one or if we use a power of two modulo. In the case of the
   * power of two modulo, we just mask the least significant bytes, we just have
   * to check that the truncated_hash_type didn't truncated too much bytes.
   */
  template <class T = size_type,
            typename std::enable_if<
                std::is_same<T, truncated_hash_type>::value>::type* = nullptr>
  static bool USE_STORED_HASH_ON_REHASH(size_type /*bucket_count*/) {
    return StoreHash;
  }

  template <class T = size_type,
            typename std::enable_if<
                !std::is_same<T, truncated_hash_type>::value>::type* = nullptr>
  static bool USE_STORED_HASH_ON_REHASH(size_type bucket_count) {
    (void)bucket_count;
    if (StoreHash && is_power_of_two_policy<GrowthPolicy>::value) {
      tsl_hh_assert(bucket_count > 0);
      return (bucket_count - 1) <=
             std::numeric_limits<truncated_hash_type>::max();
    } else {
      return false;
    }
  }

  /**
   * Return an always valid pointer to an static empty hopscotch_bucket.
   */
  hopscotch_bucket* static_empty_bucket_ptr() {
    static hopscotch_bucket empty_bucket;
    return &empty_bucket;
  }

 private:
  buckets_container_type m_buckets_data;
  overflow_container_type m_overflow_elements;

  /**
   * Points to m_buckets_data.data() if !m_buckets_data.empty() otherwise points
   * to static_empty_bucket_ptr. This variable is useful to avoid the cost of
   * checking if m_buckets_data is empty when trying to find an element.
   *
   * TODO Remove m_buckets_data and only use a pointer+size instead of a
   * pointer+vector to save some space in the hopscotch_hash object.
   */
  hopscotch_bucket* m_buckets;

  size_type m_nb_elements;

  /**
   * Min size of the hash table before a rehash can occurs automatically (except
   * if m_max_load_threshold_rehash os reached). If the neighborhood of a bucket
   * is full before the min is reacher, the elements are put into
   * m_overflow_elements.
   */
  size_type m_min_load_threshold_rehash;

  /**
   * Max size of the hash table before a rehash occurs automatically to grow the
   * table.
   */
  size_type m_max_load_threshold_rehash;

  float m_max_load_factor;
};

}  // end namespace detail_hopscotch_hash

}  // end namespace collie

#endif
